Cable terminal for use with electron gun apparatus



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G. R. KOC H Nov. 15, 1966 CABLE TERMINAL FOR USE WITH ELECTRON GUN APPARATUS Filed June 1, 1965 5 Sheets-Sheet 5 r Z EM 5 m i Patented Nov. 15, 1966 3,286,021 CABLE TERMINAL FOR USE WITH ELECTRON GUN APPARATUS George Robert Koch, Los Altos, Calif-2, assignor to Temescal Metallurgical Corporation, Berkeley, Calif.,

a corporation of California Filed June 1, 1965, Ser. No. 460,436 7 Claims. (Cl. 174-80) The present invention relates generally to terminals for high voltage cables and more particularly is directed to a terminal for a high voltage coaxial cable adapted for supplying power to electrical apparatus employed in a high. vacuum enclosure.

When electrical apparatus are employed in high vacuum enclosures, it is necessary to penetrate the walls of the enclosure in order to supply power tothe electrical apparatus. For example, electrical apparatus such as electron beam guns in high vacuum furnaces have been employed in numerous operations, such as purification of metals, annealing, vapor-plating, etc. The electron bea-in gun provides a beam of electrons which is directed at the material to be treated, the electron gun and the material being treated being disposed within an evacuated enclosure. The electron gun typically includes a source of electrons, such as a heated cathode or filament, and an accelerating electrode which is maintained at a high positive potential relative to the cathode, thereby resulting in the establishment of a high electrostatic field for accelerating the electrons. In addition, a focusing electrode is usually provided in the electron gun for focusing the electrons into a beam. The electron beam is then directedonto the target material thereby heating it.

Numerous difiiculties arise in providing electrical connection between the source of power and the electron :gun bcause of the high currents and high potentials required in an electron beam gun apparatus. Also, the electrical connections penetrate the wall of the evacuated enclosure, and therefore preferably are provided with vacuum-tight seals. The insulating and shielding means associated with the electrical connections quickly lose their proper-ties in the vapor filled and highly corrosive environments of a high vacuum furnace. In addition, radio frequency fields are generated in the furnace as a result of the excited state of the vapors present, which excited state is caused by the interaction of electrons within the vapor. The electrical connections are preferably shielded from these fields so as to prevent the same from affecting other associated electrical equipment. Moreover, the electrical connections must he such that personnel are protected from the high voltages used.

It is an object of the present invention to provide a terminal structure for a coaxial cable adaptable for supplying power to electrical apparatus disposed in a highly evacuated enclosure.

It is another object of the present invention to provide a compact terminal structure for a coaxial cable adaptable for supplying high levels of current and voltage to an electron gun disposed in an evacuated chamber.

It is another object of the invention to provide a compact and durable terminal structure for a coaxial cable for supplying power to an electron gun which terminal structure is provided with self-contained vapor shielding and high voltage insulation.

It is a further object to provide a terminal structure for a coaxial cable which structure supports and supplies power to an electron gun in an electron furnace.

Other objects and advantages of the present invention will become apparent from the following detailed description when considered in conjunction with the accompanying drawings wherein:

FIGURE 1 is a schematic vertical cross-sectional view of one embodiment of the present invention;

FIGURE 2 is a vertical cross-sectional view of another embodiment of terminal structure constructed in accordance with the principles of the present invention, which is particularly adaptable for use with a plurality of electron beam guns in an electron beam furnace;

FIGURE 3 is a view taken along line 3-3 of FIG- URE 2; and

FIGURE 4 is a vertical cross-sectional view of another embodiment of the terminal structure.

A coaxial cable constructed in accordance with the principles of the present invention is adaptable for use in conjunction with applications requiring the supply of relatively high voltages to electrical apparatus disposed in a high vacuum system. But, since it is particularly advantageous for supplying power to an electron gun in a high vacuum electron furnace, it i described in terms thereof.

Referring to the drawings and particularly to FIG- URE 1, which illustrates a coaxial cable constructed in accordance with the present invention disposed in a vertical position, the cable generally includes a central conductor 10, a second tubular conductor 14 disposed concentrically about the central conductor 10 and insulated therefrom by a sleeve 1-8 of insulation, a second sleeve 22 of insulation disposed on the first tubular conductor, and a third tubular conductor 26, which terminates a predetermined distance from the end of the cable, disposed about the second sleeve of insulation 22. The terminal portion of the cable includes means 30 for connecting the central conductor 10 and the second tubular conductor 14 to a filament 34 of the electron gun and a generally cup-shaped vapor shield 38, fabricated of a conductive material. The vapor shield 38 is provided with an aperture 42 in its base 46- through which the second tubular conductor 14 and the central conductor 10 extend, with the second tubular conductor 14 being in electrical communication with the vapor shield 38. In addition, the vapor shield 38 substantially enclose the sleeve 22 of insulation and is main-tained in spaced relationship to the sleeve 22 and to the third tubular conductor 26.

More specifically, the coaxial cable is adapted to supply both the power for operating the filament of the electron gun and the accelerating high voltage thereof. The cable extends into an evacuated enclosure (not shown) commonly referred to as an electron gun chamber in substantially vacuum-tight relationship therewith. The end of the cable is provided with a terminal which connects the cable to the electron gun. The terminal shown in FIGURE 1 is particularly adapted to support an electron beam gun and cool the same as well as supplying power thereto. The illustrated electron gun is generally similar to that disclosed in the pending application Serial No. 362,264, filed April 24, 1964, entitled, Electron Furnace.

Preferably a cooling tube 50 is provided for supplying a suitable cooling fluid to cool the electron gun. The cooling tube 50 is disposed within the central conductor 10, and is maintained in spaced relationship therewith, terminating adjacent a focusing electrode 54 of the electron gun, which focusing electrode is a generally rectangular block of conductive material. Thus, the coolant, which is preferably water, may flow out through the open end of the tube 50 and return to a suitable sink (not shown) through the annular spacing 52 between the tube 50 and the central conductor 10. The tube 50 is fabricated of a non-conductive material, such as nylon, to

prevent arcing between the central conductor and the tube 50.

The central conductor 10 is electrically coupled to the focusing electrode 54 which, in turn, is electrically connected to one end of the rod-shaped filament 34. As shown, the central conductor 10 extends into an aperture 58 provided in the focusing electrode 54 and thereby also serves to support the focusing electrode 54. The central conductor 10 is vacuum sealed to the walls of aperture 58 by suitable means such as brazing. The central conductor 10 is disposed concentrically about the cooling tube 50, and is preferably fabricated of a tube of conductive material such as copper.

The second tubular conductor 14 communicates with the other end of the filament 34 to thereby heat the same. The second tubular conductor 14 is disposed concentrically about the central conductor 10, being spaced therefrom by the first sleeve of insulation 18. The second tubular conductor 14 terminates a predetermined distance below the end of the central conductor 10.

Because of the high vacuum in the enclosure, it is preferable to construct the end of cable so that it is vacuum tight. In this connection, a first vacuum-tight seal 59 is provided between the second conductor 14 and the central conductor 10. The vacuum-tight seal includes an annular sleeve of suitable insulation 62, such as alumina, disposed intermediate the end of the second tubular conductor 14 and the central conductor 10. The sleeve of insulation is maintained in position by disposing a pair of spider cups 66 and 68 at its upper and lower ends and the cups are respectively vacuum sealed to the central conductor 10 and the second tubular conductor 14 by suitable means such as brazing.

A terminal 72 is provided on the second tubular conductor 14 adjacent its upper end. A conductor 76 is connected between the terminal 72 and the filament 34, for electrically connecting the second tubular conductor to the filament 34. An insulating spacer 80, fabricated of a suitable insulation, such as Teflon, is disposed intermediate a portion of the filament 34 and the focusing electrode 54 as shown. Thus, a complete electrical circuit is provided between the second tubular conductor 14 and the central conductor 10. This circuit extends from the terminal 72 adjacent the end of the second tubular conductor 14, through the conductor 76, through the filament 34, and through the focusing electrode 54 to the central conductor 10.

Since the voltage drop across the filament 34 is relatively low, the central conductor 10 and the second tubular conductor 14 are generally at very nearly the same potential. Thus, the first sleeve of insulation 18, disposed intermediate the central conductor 10 and the second tubular conductor 14, may be relatively thin.

A rod-shaped accelerating electrode 84 of the electron gun is generally disposed adjacent to the focusing electrode 54 and parallel to the filament 34. The accelerating electrode 84 is maintained at a very high positive potential with respect to the focusing electrode 54, thereby establishing an electrostatic field through which electrons emitted from the filament 34 are accelerated. This is accomplished through maintaing the electrode 84 at ground potential by coupling it to the third tubular conductor 26, which is grounded. In this connection an annular flange 88 is provided on the third tubular conductor 26 adjacent its end, and is preferably brazed thereto. A generally U- shaped, conductive support structure 92 is secured to the third tubular conductor 26 adjacent the flange 88 preferably by soldering. The support structure 92 extends upwardly and is secured to the accelerating electrode 84 by disposing the electrode 84 in a pair of opposed slots 94 and 95 provided in the walls of the structure 92, thereby supporting the accelerating electrode 84 as well as electrically connecting it to the grounded third tubular conductor 26. Since the filament 34 is supplied with a relatively high negative potential, while the accelerating electrode 84 is maintained at ground potential, the accelerating electrode 84 is at high positive potential with respect to the filament 34, thus establishing the requisite electrostatic field.

Since there is substantial difference in potential between the second tubular conductor 14 and the grounded third tubular conductor 26, the sleeve of insulation 22 disposed therebetween is relatively thick to preclude the occurrence of arc-over. The sleeve of insulation 22 extends beyond the flanged end of the third tubular conductor 26, terminating between the end of the third tubular conductor 26 and the end of the second tubular conductor 14. The sleeve of insulation 22 is preferably fabricated of a relatively stable material having a low vapor pressure, such as Teflon.

A second vacuum seal 99 is provided between the third conductor 26 and the second conductor 14. The seal 99 also provides substantial mechanical support for the end of the cable. The vacuum seal 99 includes a high voltage insulating bushing 100 mounted on the flange 88, and disposed about a predetermined portion of the insulating sleeve 22 extending above the flange 88.

The bushing 100 is secured at its lower end to the flange 88 by a spider cup 104, and is secured at its upper end to the first tubular conductor 14 by a second spider cup 108. Preferably the spider cup 104 is vacuum sealed to the flange 88 by suitable means such as brazing. In addition, the spider cup 108 is preferably vacuum sealed to the second tubular conductor 14 and to the bushing 100, thereby completing the vacuum seal between the third tubular conductor 26 and the second tubular conductor 14. The bushing 100 is in the form of an annular sleeve of high voltage insulation, fabricated of a material such as alumina and has a generally ridge-shaped outer surface. The ridge-shaped outer surface is desirable in that it increases the creepage distance along the surface of the insulation and thereby prevents the occurrence of arc-over.

Since the bushing 100 is provided to minimize the existence of voltage creepage and thereby provide protection against arc-over by increasing the creepage distance, it is advantageous to protect the ridged surface of the bushing so that it retains its insulating properties. Such a protection is particularly desirable in view of the presence of conductive vapors in an electron furnace, which might be deposited on the surface of the bushing 100. Thus, the vapor shield 38 is provided.

The vapor shield 38 is disposed about the insulating bushing 100 so as to substantially enclose it. The vapor shield 38 is generally in the form of an inverted cup with its base 46 positioned above the upper end of the bushing 100 and being electrically connected to the second tubular conductor 14, and its lip portion being adjacent the lower end of the bushing 100. Since the shield 38 is electrically connected to the second tubular conductor 14 it is maintained at a relatively high negative potential and thus serves to protect the insulating bushing 100, which it encloses, from the deposition of conductive vapors. The vapor shield 38 is fabricated of a non-corrosive material, such as tantalum.

The terminal structure described above provides a durable shielded structure for supplying high levels of vol-tage to an electron gun, while minimizing the occurrence of arc-over. In addition, the particular configuration provides substantial shielding of the terminal structure from radio frequency pick up by providing a large shunting capacitance between the central and first tubular conductors and ground, thereby reducing the radio frequency components conveyed to other circuit elements. In this connection, the lower edge of the vapor shield 38, which is at a high negative potential, is positioned relatively close to the flange 88 which is at ground potential. Because of this decreased spacing the capacitance is relatively high.

In FIGURE 2 a second embodiment of the present invention is shown, disposed in a generally vertical position, in which corresponding parts are designated by the same reference numerals as used in FIGURE 1, but followed by the letter a.

The end of the cable is provided with a terminal for connecting the cable to an electron gun so as to provide support for the electron gun, if such is desired, as well as to supply power to it.

If desired a suitable coolant tube (not shown) may be disposed concentrically within the central conductor a for providing cooling of the focusing electrode structure of the electron gun.

The second sleeve of insulation 22a which is disposed intermediate the second tubular conductor 14a and the grounded third tubular conductor 26a extends a predetermined distance beyond the upper end of the third tubular conductor 26a, terminating below the upwardly extending end of the second tubular conductor 14a.

However, the second tubular conductor 14a is supplied with a very high potential with respect to ground. Thus, the insulating properties of the second sleeve of insulation 22a again afford insuflicient protection against the eventua-l occurrence of arc-over between the portion of the second tubular conductor 14a, which extends beyond the second sleeve of insulation 22a, and the upper end of the grounded third tubular conductor 26a, as a result of the occurrence of voltage creepage. Thus, an elongated tubular high voltage ceramic insulator 112 is disposed in spaced relationship about the upper portion of the second sleeve of insulation 22a, extending generally from the upper end of the sleeve 22a to the upper end of the third tubular conductor 26a.

The ceramic insulator 112 is generally tubular in form, but has an inwardly extending shoulder 116 at its upper end, which terminates in a generally step-shaped portion 120 at its innermost end. The inwardly extending shoulder 116 is disposed upon the upper end of the second sleeve of insulation 22a, and is maintained in position by disposing a suitable spider cup 124 about the step-shaped portion 120 of the insulator 112. Preferably the spider cup 124 is vacuum sealed to the portion 120 and to the second tubular conductor 14a by suitable means, such as brazing. Suitable support for the lower end of the ceramic insulator 112 is provided by disposing a spider cup 128 about the lower end of the insulator 112. The spider cup 128 is also preferably vacuum sealed into position by suitable means, such as brazing. The ceramic insulator 112 is fabricated of a material which exhibits good structural strength as Well as excellent electrical insulating properties, such as a high density alumina cylinder.

Support is provided for the spider cup 128, which maintains the lower end of the insulator 112 in position, by disposing a relatively short cylindrical support member 132 in tight-fitting relationship about the exterior of the spider cup 128, and brazing the connection. The lower end of the support member 132 is suitably secured within a stepped portion 136 provided on the outer end of the annular flange 88a. The flange 88a is preferably soldered to the end of the third tubular conductor 26a and supported by the support member 132. The upper end of the support member 132 is secured to a rigid, grounded support structure 140 preferably fabricated of steel. Preferably an O-ring seal 141 is provided intermediate the support member 132 and the grounded support structure 140 to maintain a vacuum-tight seal therebetween. The support member 132 is fabricated of rigid, conductive material such as steel and thus couples the end of the third tu'bular conductor 26a to ground.

The voltage gradient along the surfaces of the insulator 112 tends to be greatest at its lower end where it is adjacent to the grounded flange 88a. Thus, the electric field is more concentrated in this region and corona discharge may occur. To minimize this possiblity means are provided to optimize the voltage gradient along these surfaces, making it as low as possible, thereby preclud ing concentration of the electric field, so that corona discharge .is unlikely to occur. Thus, a generally tubular voltage gradient controller 144 is disposed within the lower portion of the spacing intermediate the insulator 112 and the insulating sleeve 22a and is maintained in spaced relationship with both the insulator 112 and the insulating sleeve 22a. The lower end of the voltage gradient controller 144 is disposed in a slot 146 on the surface of the flange 88a and is thereby grounded. The upper end of the voltage gradient controller 144 extends beyond the lower end of the vapor shield 38a. The voltage gradient controller 144 is fabricated of a material such as steel, and serves to optimize the voltage gradient along the inner surface of the ceramic insulator 112, making it as low as possible so as to prevent arc-over.

A voltage gradient controller 148 generally similar to the voltage gradient controller 144 is disposed about the exterior of the insulator 112 so as to similarly optimize the voltage gradient along the exterior surface of the insulator 112. The lower end of the voltage gradient controller 148 has an outwardly extending shoulder 152 which is disposed within a slot 156 defined by the inner end of the support structure and an inwardly extend ing shoulder 160 on the support member 132. The lower end of the voltage gradient controller 148 is thus electrically coupled to the grounded support structure 140. The upper end of the voltage gradient controller 148 extends upwardly approximately the same distance as the voltage gradient controller 144. The wall of the voltage gradient controller 148, which is also fabricated of steel, is of generally tapered thickness, such that it is thinner at its top and thicker at its bottom. As a result the upper portion of the wall of the voltage gradient controller 148 is spaced further from the ceramic insulator than is the bottom portion of the wall. This is advantageous since the voltage along the surface of the ceramic insulator 112 tends to be greatest along its upper portion, where it is closer to the upper end of the high voltage second tubular conductor 14a.

It is advantageous to provide protection for the surfaces of the high voltage insulator 112 in view of the vaporous environment in an electron beam furnace. If such a protection were not furnished conductive vapors might be deposited on the insulator 112 causing it to lose some of its insulating properties and possibly resulting in the occurrence of arc-over. Thus, the vapor shield 38a is provided which is generally in the form of an inverted cup comprising a base 164 having an aperture 168 and a cylindrical downwardly extending wall 172, secured to the base 164 by suitable rivets 176. The base 164 is disposed about the second tubular conductor 14a, and is maintained in position by securing it to a generally tubular steel support structure having an inwardly extending shoulder 182, which is secured to the lip 184 of a copper bushing 188, disposed about the second tubular conductor 14a. The bushing 188 is preferably soldered to the second tubular conductor 14a and is maintained in electrical contact therewith. A cap screw 192 is inserted through corresponding apertures 196 in the base 164, the support structure 180 and the lip 184, and thereby maintains the base 164 in position. The cylindrical wall of the vapor shield 38a is of a larger diameter than the voltage gradient controller 148 and extends downwardly, terminating below the upper end of the voltage gradient controller 148, thereby enclosing the insulator 112.

Since the base 164 of the vapor shield 38a is electrically coupled to the second tubular conductor 14a through the copper bushing 188, the vapor shield 38a is maintained at a very high negative potential with respect to ground and thereby serves to protect the insulator 112 from the deposition of conductive vapors on its surface. Moreover, the steel support structure 180 which is disposed about the upper end of the insulator 112 serves as an additional voltage gradient controller to optimize the voltage gradient along the upper portion of the exterior surface of the insulator 112 and prevent areover.

It is advantageous in certain instances to provide conductive clamp 208 and 212 disposed in electrical communication with the second tubular conductor 14a and the central conductor 1011 respectively to which suitable conductors may be secured for supplying power to the filament (not shown) of the electron gun. The clamp 208 is disposed about the bushing 188, thereby communicating electrically with the second tubular conductor 14a. The clamp 208 may then be electrically coupled to the filament (not shown). The clamp 208 is tightly secured about the bushing 188 by a bolt 216.

I A generally cylindrical, conductive lead terminal 220 having a shoulder 224 is disposed within the central conductor a. The shoulder 224 extends onto the upper end of the central conductor 10a, and serves to support the lead terminal 220 in its position in electrical contact with the central conductor 10a. The clamp 212 is disposed about the upper end of the lead terminal 220 in electrical communication therewith and is tightly secured thereto by a bolt 228. The clamp 212 may then be electrically coupled to the cathode (not shown).

To prevent the occurrence of arc-over between the lead terminal 220 and the bushing 188 an insulating sleeve 232 of a material such as Teflon is disposed substantially about the portion of the lead terminal 220 which is intermediate the clamp 212 and the upper end of the central conductor 10a. The sleeve 232 is maintained in position by disposing a spider cup 236 extending between the sleeve 232 and a shoulder 240 provided on the upper end of the bushing 188. The spider cup 236 is preferably vacuum sealed to the insulating sleeve 232 and to the shoulder 240 by suitable means, such as brazing.

In order to protect the insulating sleeve 232 from the deposition of a conductive coating on its surface, which would impair its insulating properties, a relatively small vapor shield 242 preferably fabricated of tantalum is disposed substantially about the sleeve 232. The shield 242 is secured to a support structure 244 disposed on the upper end of the sleeve 232.

It is generally desirable to prevent the occurrence of corona discharge in the spaces or voids present in the terminal structure. A suitable high dielectric strength material, preferably silicon grease is pumped into these voids through an aperture 248 provided in the flange 88a. The aperture 248 is then appropriately plugged or sealed by a plug 252, positioned within the aperture 248.

Thus, a cable and terminal have been provided containing shielding from the corrosive vapors present in an electron beam furnace and protection against arc-over so that a highly durable structure results. Moreover, the structure provides a relatively large capacitance between the high voltage conductors and ground, which results in shunting radio frequency components to ground, preventing adverse effects on other circuit elements.

Another embodiment of the present invention is shown in FIGURE 4, disposed in a generally vertical position. This embodiment is generally similar to the embodiment shown in FIGURES 2 and 3, and corresponding parts are designated by the same numerals as used in FIGURE 2, followed by the letter b. This embodiment is particularly adaptable for providing excellent shielding against coating by vaporous material, as well as producing a low voltage gradient on the surface of the ceramic insulator 11212. In this embodiment, a voltage controller is not provided between the ceramic insulator 1121) and the sleeve of insulation 22]). Therefore, the diameter of the insulator 1121; is only slightly larger than the diameter of the sleeve of insulation 22b.

If it is desired to provide cooling for the focusing electrode structure of the electron gun, a suitable coolant tube (not shown) may be disposed concentrically within the central conductor 10b.

The annular flange 88b, which is preferably soldered to the third tubular conductor 26b, is provided with a generally tubular portion 254, which extends upwardly to approximately the upper surface of the support member 1401). The tubular portion 254 encloses the lower end of the insulator 112b. The flange 88b serves as a support structure for the insulator 11217. In this connection a spider cup 255 is disposed between an upwardly extending lip 256 provided on the upper end of the tubular portion 254 and the insulator 112b, and is preferably vacuum sealed into position by suitable means, such as brazing. Another spider cup 258 is disposed about the upper end of the insulator 112b, and similarly is preferably vacuum sealed into position by suitable means, such as brazing.

The flange 88b is provided with an outwardly extending shoulder portion 260 which is disposed adjacent the lower end of the grounded support structure 14012 The flange 88b is tightly secured to the support structure 14012 by disposing an annular flange 264 below the shoulder portion 260 and securing the annular flange 264 to the support structure 14012 by suitable screws 268. In addition, an O-ring seal 270 is preferably provided intermediate the shoulder portion 260 and the grounded support structure 1401) so as to provide a vacuum-tight seal therebetween.

In order to provide protection against voltage creepage, which may occur on the outer surface of the insulator 112b, a voltage gradient controller 272 is disposed about the insulator 1121) and is spaced therefrom. The lower end of the voltage gradient controller 272 is disposed about the exterior of the lip 256 on the member 254 and is thereby maintained at ground potential, while the upper portion of the voltage gradient controller extends upwardly, terminating below the upper end of the insulator 1121:.

The vapor shield 38b is disposed about the voltage gradient controller 272 and the insulator 11211. The wall 172b of the vapor shield 38b extends downwardly, terminating below the upper end of the voltage gradient controller 272.

Support for the vapor shield 38b is provided by a bushing 276 disposed about the upper end of the second tubular conductor 14b and maintained in electrical communication therewith. The bushing 276 is provided with a flange 280 adjacent its lower end. A tubular vapor shield support structure 284 having an inwardly extending shoulder 288 is disposed on the flange 280, with the shoulder 288 resting on the flange 280. The support structure 284 extends downwardly, terminating adjacent the upper end of the insulator 112b, and thus serves as an additional voltage gradient controller to optimize the voltage gradient on the upper end of the insulator 11212. The base 16411 of the vapor shield 38b is then disposed on the upper surface of the shoulder 288, and is electrically coupled to the second tubular conductor 14b through the bushing 276. The vapor shield 38b is thus maintained at a high negative potential with respect to ground and serves to protect the insulator 11211 from the deposition of conductive vapors on its surface.

To prevent the occurrence of corona discharge a suitable dielectric material such as silicon grease is disposed in the spaces and voids in the terminal structure. Thus, the flange 88b is provided with the aperture 24% through which the silicon grease may be pumped into the spaces. The plug 252b is then disposed in the aperture 248b, sealing it.

Thus, a cable terminal has been provided having nu- 0'1161'0115 advantages, as previously described. Although the cable tenminal has been described as being particularly useful for supplying power to an electron beam gun in a high vacuum furnace, it should be noted that a cable terminal in accordance with the principles of the present invention is adaptable for supplying power to numerous other devices. For example, it may advantageously be employed for supplying power to accelerators, nuclear fusion devices and a wide variety of other electrical apparatus disposed in evacuated enclosures, especially when the walls of the enclosure are penetrated and it is desired to maintain the vacuum.

Various other changes and modifications may be made in the above-described terminal without deviating from the spirit and scope of the present invention.

Various features of the invention are set forth in the following claims.

What is claimed is: a

1. A tenminal for a high voltage coaxial cable adapted for supplying power to a filament and an accelerating electrode of an electron gun disposed in a high vacuum electron furnace which cable includes a central conductor, a second tubular conductor disposed concentrically about said central conductor and insulated there-from, a sleeve of insulation disposed on said second tubular conductor, and a third tubular conductor disposed about said sleeve and terminating in spaced relation to the end of said cable, said terminal comprising means for connecting said central conductor and said second tub-ular conductor to the filament of said electron gun in vacuum sealed relationship therewith, and a generally cup-shaped vapor shield of conductive material having an aperture in its base through which said second tubular conductor and said central conductor extend, said shield being in electrical communication with said second tubular conductor and substantially enclosing said insulating sleeve in spaced relationship to said sleeve and said third tubular conductor.

2. A terminal for a high voltage coaxial cable adapted for supplying power to a filament and an accelerating electrode of an electron gun disposed in a high vacuum electron furnace which cable includes a central conductor, a second tubular conductor disposed concentrically about said central conductor, a relatively thin first sleeve of insulation disposed intermediate said central conductor and said second tubular conductor, a relatively thick second sleeve of insulation disposed on said second tubula'r conductor, and a third tubular conductor disposed about said second sleeve of insulation terminating in spaced relation to the end of said cable to thereby provide an uncovered portion of said second sleeve of insulation said tenminal comprising means for connecting said central conductor and said second tubular conductor to the filament of said electron gun in vacuum sealed relationship therewith, means for connecting said third tubular conductor to the accelerating electrode of said electron gun, a sleeve of high voltage ceramic insulation disposed about said uncovered portion of said second sleeve of insulation and maintained in vacuum sealed relationship therewith, said sleeve of high voltage ceramic insulation having a generally ridge-shaped outer circumferential surface to minimize voltage creepage along the surface thereof, and a generally cup-shaped vapor shield of conductive material having an aperture in its base through which said second tubular conductor and said central conductor extend, said shield being in electrical communication with said second tubular conductor and substantially enclosing said sleeve of high voltage ceramic insulation in spaced relationship to said sleeve and said third tubular conductor.

3. A terminal for a high voltage coaxial cable adapted for supplying power to a filament and an accelerating electrode of an electron gun disposed in a high vacuum electron furnace which cable includes a central conductor, a second tubular conductor disposed concentrically about said central conductor, a relatively thin first sleeve of insulation disposed intenmediate said central conduct-or and said second tubular conductor, a relatively thick second sleeve of insulation disposed on said second tubular conductor, and a third tubular conductor disposed about said second sleeve of insulation terminating in spaced relation to the end of said cable to thereby provide an uncovered portion of said second sleeve of insulation, said terminal comprising means for connecting said central conductor and said second tubular conductor to the filament of said electron gun in vacuum sealed relationship therewit'h, a sleeve of high voltage ceramic insulation disposed about said uncovered portion of said second sleeve of insulation and said second tubular conductor, said sleeve of high voltage ceramic insulation being maintained in spaced relationship with said second sleeve of insulation and said second tubular conductor, means for providing a vacuum seal between said third tubular conductor and said second tubular conductor, a first sleeve of conductive material disposed intermediate said sec-ond sleeve of insulation and said sleeve of ceramic insulation and spaced therefrom, a second sleeve of conductive material disposed about the exterior of said sleeve of ceramic insulation and spaced therefrom, means for electrically connecting one end of said first sleeve of conductive material and of said second sleeve of conductive material to ground, and a generally cup-shaped vapor shield of conductive material having an aperture in its base through which said second tubular conductor and said central conductor extend, said shield being in electrical communication with said second tubular conductor and enclosing said sleeve of high voltage ceramic insulation and the other end of said second sleeve of conductive material in spaced relation thereto.

4. A terminal for a high volt-age coaxial cable adapted for supplying power to a filament and an accelerating electrode of an electron gun disposed in a high vacuum electron furnace which cable includes a central conductor, a second tubular conductor disposed concentrically about said central conductor, a relatively thin first sleeve of insulation disposed intermediate said central conductor and said second tubular conductor, a relatively thick second sleeve of insulation disposed on said second tubular conductor, and a third tubular conductor disposed about said second sleeve of insulation terminating in spaced relation to the end of said cable to thereby provide an uncovered portion of said second sleeve of insulation, said terminal comprising means for connecting said central conductor and said second tubular conductor to the filament of said electron gun, a sleeve of high voltage ceramic insulation disposed about said uncovered portion of said second sleeve of insulation, a tubular member of conductive material disposed about said sleeve of ceramic insulation and spaced therefrom, means for electrically coupling one end of said tubular member of conductive material to ground, and a generally cupshaped vapor shield of conductive material having an aperture in its base through which said second tubular conductor and said central conductor extend, said shield being in electrical communication with said second tubular conductor and enclosing said sleeve of ceramic insulation and the other end of said tubular member in spaced relation thereto.

5. A terminal for a high voltage coaxial cable adapted for supplying power to a filament and an accelerating electrode of an electron gun disposed in a high vacuum electron furnace which cable includes a central conductor, a second tubular conductor disposed concentrically about said central conductor, a relatively thin first sleeve of insulation disposed intermediate said central conductor and said second tubular conductor, a relatively thick second sleeve of insulation disposed on said second tubular conductor, and [a third tubular conductor disposed about said second sleeve of insulation and terminating in spaced relation to the end of said cable to thereby provide .an uncovered portion of said sleeve of insulation, said terminal comprising clamp means in electrical communication with said central conductor and said second tubular conductor for coupling said central conductor and said second tubular conductor to the filament of said electron gun, a sleeve of high voltage alumina insulation disposed about said uncovered portion of said second sleeve of insulation and being spaced therefrom, means disposed adjacent the surface of said sleeve of high voltage insulation for maintaining a low voltage gradient along the surface thereof, and a generally cupshaped vapor shield of conductive material having an aperture in its base through which said second tubular conductor and said central conductor extend, said shield being in electrical communication with said second tubular conductor and substantially enclosing a predetermined portion of said sleeve of alumina insulation in spaced relation thereto.

6. A terminal for a high voltage coaxial cable adapted for supplying power to an electrical apparatus disposed in an evacuated enclosure which cable includes a central conductor, a sleeve of insulation disposed about said central conductor, a tubular conductor disposed concentrically about said insulated central conductor, said tubular conductor terminating in spaced relation to the end of said cable to provide an uncovered portion of said sleeve of insulation, said terminal comprising means for connecting said central conductor and said tubular conductor to said electrical apparatus, a sleeve of high voltage ceramic insulation disposed about said uncovered portion of said sleeve of insulation, a first sleeve of conductive material disposed intermediate said sleeve of insulation and an inner surface of said sleeve of ceramic insulation and spaced therefrom for optimizing the voltage gradient along said inner surface, a second sleeve of conductive material disposed about the exterior of said sleeve of ceramic insulation and spaced therefrom for optimizing the voltage gradient along said exterior of said ceramic insulation, and means for electrically connecting one end of said first sleeve of conductive material and of said second sleeve of conductive material to ground.

7. A terminal for a high voltage coaxial cable adapted for supplying power to an electrical apparatus disposed in an evacuated enclosure which cable includes a central conductor, a first sleeve of insulation disposed about said central conductor, a second conductor disposed about said insulated central conductor, said second conductor terminating in spaced relation to the end of said cable to provide an uncovered portion of said first sleeve of insulation, said terminal comprising means for connecting said central conductor and said second conductor to said electrical apparatus, a sleeve of high voltage alumina insulation disposed about said uncovered portion of said first sleeve of insulation, a tubular member of conductive materal disposed about said sleeve of alumina insulation and spaced therefrom for optimizing the voltage gradient on said sleeve of alumina insulation, and means for electrically coupling one end of said tubular member of conductive material to ground.

No references cited.

LARAMIE E. ASKIN, Primary Examiner. 

1. A TERMINAL FOR A HIGH VOLTAGE COAXIAL CABLE ADAPTED FOR SUPPLYING POWER TO A FILAMENT AND AN ACCELERATING ELECTRODE OF AN ELECTRON GUN DISPOSED IN A HIGH VACUUM ELECTRON FURNACE WHICH CABLE INCLUDES A CENTRAL CONDUCTOR, A SECOND TUBULAR CONDUCTOR DISPOSED CONCENTRICALLY ABOUT SAID CENTRAL CONDUCTOR AND INSULATED THEREFROM, A SLEEVE OF INSULATION DISPOSED ON SAID SECOND TUBULAR CONDUCTOR, AND A THIRD TUBULAR CONDUCTOR DISPOSED ABOUT SAID SLEEVE AND TERMINATING IN SPACED RELATION TO THE END OF SAID CABLE, SAID TERMINAL COMPRISING MEANS FOR CONNECTING SAID CENTRAL CONDUCTOR AND SAID SECOND TUBULAR CONDUCTOR TO THE FILAMENT OF SAID ELECTRON GUN IN VACUUM SEALED RELATIONSHIP THEREWITH, AND A GENERALLY CUP-SHAPED VAPOR SHIELD OF CONDUCTIVE MATERIAL HAVING 